NFA firearms have an artificially high value because of the exact set of legal restrictions that the government has put in place: loose enough to not crater legal demand, yet tight enough to restrict legal supply. This market is tied to within US borders.
The government can destroy the assumptions behind this market with a stroke of the pen.
The government can destroy the assumptions on which many businesses are built, that are held as stocks in an investment portfolio. Move the goalposts to relation to international markets, and I will likely find how it applies to some other asset commonly found in investment portfolios, like perhaps the current values of some tax preparation companies.
Your original assertion was "...by buying NFA machine guns knowing the number is capped and the price is likely to only go up"
Later you said lower risk than many individual stocks. Maybe, maybe not depending on how we define things. But I do think it's quite possible for the price to go down.
